How is equity delivery charge calculated in groww as I got deducted higher than what they have mentioned

Today is the first day I have invested in my life. I have opened a demat account in Groww in November, in which it said that for equity delivery they will charge either 0.1% or ₹20 which is lower. I bought 200 shares at the price of ₹28.50 it’s total is ₹5700 and 1% on the same is ₹5.7 adding 18% gst gives ₹6.726 but I got deducted ₹5712.54. Why there is a difference? Can anyone help me in this regard as I am new to this?